Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via code word channels
Reexamination Certificate
1998-08-28
2002-03-19
Marcelo, Melvin (Department: 2733)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via code word channels
C360S060000, C380S203000, C386S349000
Reexamination Certificate
active
06359905
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for detecting a spectrum spread signal of an additional information signal superimposed on a main information signal of an image signal by being spectrum-spread.
BACKGROUND OF THE INVENTION
Digital information apparatuses such as a digital VTR (Video Tape Recorder), MD (Minidisc) recording and reproducing apparatuses have been spread and further, DVD (Digital Video Disc or Digital Versatile Disc) apparatuses having recording function have shown up. According to the digital information recording apparatuses, various additional information signals can be recorded by being added to a digital image signal or a digital audio signal as well as data for a computer or the like as a major information signal.
FIG. 1
shows an example of a constitution of a conventional recording apparatus for recording an additional information signal by adding it to a digital information signal. According to the recording apparatus in
FIG. 1
, a digital information signal Vi is supplied to a recording apparatus
10
via an input terminal
11
and in the recording apparatus
10
, an additional information signal is added to the digital information signal Vi and stored to a record medium
15
.
According to the recording apparatus
10
, at an adding unit
12
, the additional information signal from an additional information generating unit
13
is added to the digital information signal Vi. In this case, the additional information signal is a digital signal and is added to the digital information signal Vi by being recorded to an area which is differentiated from the digital information signal in view of area of, for example, a header portion added to data of a block unit, or other area of TOC (Table of Contents) in the digital information signal.
The digital information signal added with the additional information signal from the adding unit
12
is recorded on the record medium
15
such as a tape or a disc by a writing unit
14
. In this case, when compressed code formation of the digital information signal is needed as mentioned above, a processing of the compressed code formation is carried out at the writing unit
14
.
As described above, in the case of the conventional recording system of additional information signal, the additional information signal is not directly superimposed on the digital information signal of the header portion or the like but is added to an indirect portion. Therefore, the additional information signal is removed comparatively easily by filtering or alteration and in a recording apparatus or a reproducing apparatus, necessary additional information signal may not be detected. Particularly, when as an additional information signal, control information for preventing unfair copying, copy right information or the like is added, for removing such an additional information signal, a state where an original object cannot be achieved is brought about.
Further, in the case where an additional information signal is added to an indirect portion as mentioned above, when a digital information signal is converted into an analog signal, only a main information signal is obtained and therefore, the additional information signal is detached. Thereby, even when a copying preventive control signal as mentioned above is superimposed by which a countermeasure capable of preventing a digital information signal from being unfairly copied, is provided, when the digital signal is converted into an analog signal, the copying preventive countermeasure is no more effective.
As a system of superimposing an additional information signal for resolving the problem of detachment of the additional information signal and the problem which is caused when the digital signal is converted into an analog signal as mentioned above, the applicant has proposed a system where an additional information signal such as a copying preventive control signal or the like is spectrum-spread and the spectrum-spread additional information signal is superimposed on an image signal and the image signal is recorded by digital recording or analog recording (U.S. patent application Ser. No. 08/75510).
According to the system, a code of PN (Pseudorandom Noise) series which is used as a spread code, is generated at sufficiently high rate and is multiplied with an additional information signal to thereby spectrum-spread the code and the additional information signal of a copying preventive control signal or the like having a narrow band at a high level is converted into a signal having a wide band at a very small level which does not effect influence on an image signal or a vocal signal. Further, the additional information signal which has been spectrum-spread, that is, the spectrum spread signal is superimposed on an analog image signal and is recorded in a record medium. In this case, either of an analog and a digital signal is feasible as an image signal recorded in a record medium.
According to the system, an additional information signal of a copying preventive control signal or the like is spectrum-spread and is superimposed on an image signal as a signal at a very small level and therefore, it is difficult for, a person trying to illegally copy the signal to remove the superimposed copying preventive control signal from the image signal.
In the meantime, the additional information signal such as a superimposed copying preventive control signal or the like can be detected and utilized by subjecting the signal to inverse spectrum spreading. Accordingly, for example, not only is the copying preventive control signal firmly provided to the side of a recording apparatus along with the image signal but also on the side of the recording apparatus, the copying preventive control signal can be detected and decoding control, in accordance with the detected copying preventive control signal, can firmly be carried out.
As mentioned above, in reproducing the main information signal, the additional information signal superimposed on the main information signal such as an image signal, cannot be removed from the main information signal and accordingly, a spectrum spread signal needs to superimpose at a very small level which does not effect influence on a reproduced output of the main information signal.
However, when the spectrum spread signal is superimposed on the main information signal at such a very small level, it is important that the spectrum spread signal can be detected firmly from the main information signal.
An evaluation function
in the case of inverse spectrum spreading where a spectrum spread signal is detected from a signal Si produced by superimposing a spectrum spread signal on a main information signal is specified as follows.
=&Sgr;
si·pi
=&Sgr;(
Vi+ki·pi
)
pi
=&Sgr;
Vi·pi+&Sgr;ki·pi·pi
(1)
where notation Vi designates a main information signal such as an image signal or the like, notation pi designates a spread code such as a PN code or the like and notation ki designates a coefficient, respectively.
In Equation (1), the first term represents correlation between the main information signal and the spread code and the second term represents correlation between the spectrum spread signal and the spread signal. It is known from Equation (1) that when there is no correlation between the main information signal and the spread signal, the spectrum spread signal can easily be detected.
However, actually, the main information signal such as an image signal or the like is not uncorrelated with the spread code. That is, when the main information signal is a flat signal having no change, the main information signal is not correlated with the spread code, however, a general main information signal is changed in accordance with content of information and therefore, it cannot be uncorrelated with a PN code.
Therefore, in the case where a spectrum spread signal superimposed on a main information signal is deteriorated by, for example, undergoing influence of a low pass characteristic of a transmission path,
Ikeda Nozomu
Kimura Yuji
Kohashi Takashi
Moriwaki Hisayoshi
Ogino Akira
Maioli Jay H.
Marcelo Melvin
Sony Corporation
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